3,054 research outputs found
Depressed clad hollow optical fiber with fundamental LP01 mode cut-off
We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm
Current carrying capacity of carbon nanotubes
The current carrying capacity of ballistic electrons in carbon nanotubes that
are coupled to ideal contacts is analyzed. At small applied voltages, where
electrons are injected only into crossing subbands, the differential
conductance is . At applied voltages larger than
( is the energy level spacing of first non crossing subbands),
electrons are injected into non crossing subbands. The contribution of these
electrons to current is determined by the competing processes of Bragg
reflection and Zener type inter subband tunneling. In small diameter nanotubes,
Bragg reflection dominates, and the maximum differential conductance is
comparable to . Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than , though not
comparable to the large number of subbands into which electrons are injected
from the contacts. These results may be relevant to recent experiments in large
diameter multi-wall nanotubes that observed conductances larger than .Comment: 12 pages, 4 figure
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
We report the discovery of mesoscale regions with distinctive magnetic
properties in epitaxial LaSrMnO films which exhibit
tunneling-like magnetoresistance across grain boundaries. By using
temperature-dependent magnetic force microscopy we observe that the mesoscale
regions are formed near the grain boundaries and have a different Curie
temperature (up to 20 K {\it higher}) than the grain interiors. Our images
provide direct evidence for previous speculations that the grain boundaries in
thin films are not magnetically and electronically sharp interfaces. The size
of the mesoscale regions varies with temperature and nature of the underlying
defect.Comment: 4 pages of text, 4 figure
Remarks on Renormalization of Black Hole Entropy
We elaborate the renormalization process of entropy of a nonextremal and an
extremal Reissner-Nordstr\"{o}m black hole by using the Pauli-Villars
regularization method, in which the regulator fields obey either the
Bose-Einstein or Fermi-Dirac distribution depending on their spin-statistics.
The black hole entropy involves only two renormalization constants. We also
discuss the entropy and temperature of the extremal black hole.Comment: 14 pages, revtex, no figure
Characterization of a Plain Broadband Textile PIFA
Bandwidth characteristic of a wearable antenna is one of the major factors in determining its usability on the human body. In this work, a planar inverted-F antenna (PIFA) structure is proposed to achieve a large bandwidth to avoid serious antenna reflection coefficient detuning when placed in proximity of the body. The proposed structure is designed based on a simple structure, in order to provide practicality in application and maintain fabrication simplicity. Two different types of conductive textiles, namely Pure Copper Polyester Taffeta Fabric (PCPTF) and ShieldIt, are used in order to proof its concept, in comparison with a metallic antenna made from copper foil. The design is spaced and fabricated using a 6 mm thick fleece fabric. To cater for potential fabrication and material measurement inaccuracies, both antennas' performance are also investigated and analyzed with varying physical and material parameters. From this investigation, it is found that the proposed structure's extended bandwidth enabled the antenna to function with satisfactory on-body reflection coefficients, despite unavoidable gain and efficiency reduction
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